The goal of this application is to develop a synthetic inhibitor of elastase that will be effective and safe in the treatment of emphysema. Two different laboratories reported that chloromethyl ketone (CMK) is effective in animal models of emphysema. However, the CMK are too toxic for human use. We have modified the structure of the CMK to retain its activity and desirable physical properties but reduce its toxicity. Our initial inhibitor, a derivative of N-CBZ-phenylalanine, Ki = 3.61 +/- 0.07 x 10-5 M, was evaluated against the serine enzyme chymotrypsin. CMK reacts with glutathione leading to toxic effects. Our inhibitor does not react with glutathione. We propose to synthesize two additional inhibitors and compare them with our present inhibitor. An oligopeptide inhibitor will be synthesized based on our best inhibitor. This inhibitor will be evaluated: 1) against human neutrophil elastase using tritiated calf ligament elastin as substrate, 2) for clearance from hamster lungs, and 3) in the hamster model of emphysema using human neutrophil elastase. These oligopeptide inhibitor assays will be conducted by Drs. P. J. Stone and E. C. Lucey.